The overall project goal is to develop an orally active small molecule BoNT/A inhibitor. The neuronal substrate for BoNT/A LC is synaptosomal-associated protein of 25.000MW (SNAP-25). Our hypothesis is that small molecule BoNT/A inhibitors which can penetrate the neuron, preventing SNAP-25 cleavage by the BoNT LC, will provide the potential for treatment of both pre- and post-toxin exposure. Our strategy has been to identify "drug-like" small molecule BoNT/A LC inhibitor scaffolds, through a combination of chemical library screening and 3D sub-structure database mining, suitable for further chemical refinement in a rational drug design program. Through this process, we have identified several BoNT/A inhibitors with low uM potencies in enzymatic and cell based assays, which prevent BoNT/A intracellular proteolysis of its target substrate SNAP-25. The identified inhibitor classes are novel and devoid of non-drug like features such as hydroxamic acid and peptidic backbones. These validated chemical "hit" series will form the basis for development of efficacious, safe and orally bioavailable drugs against BoNT/A. We will apply proven techniques of medicinal and combinatorial chemistry;inhibitor-enzyme complex X-ray crystallography and structure-based drug design (SBDD) to rapidly synthesize and evaluate derivatives of these new validated BoNT/A inhibitor scaffolds. In an iterative process, we will probe focused compound libraries for features contributing to tighter binding and more potent inhibition of BoNT/A by measuring the enzymatic and cellular activity and specificity of derivatives. We will determine the X-ray structures of improved inhibitors bound to the BoNT active site, and use the data to develop refined pharmacophore models to guide further probing of the structure activity relationship (SAR). We will assess compounds for optimal ADME (Absorption, Distribution, Metabolism, Elimination), pharmacokinetic and bioavailability properties. Compounds with sufficient enzymatic, cellular potency and ADME properties will be scaled-up and tested for efficacy in a BoNT induced rat death model. Successful rescue of rats from BoNT-induced death will qualify compounds as in vivo-validated leads. We will evaluate these leads for investigational new drug (IND) enabling toxicity and safety pharmacology in order to develop them into pre-IND clinical candidates, suitable for human clinical trials. By the end of this proposed research and pre-clinical development plan, our overall project milestone is to file an IND for the clinical human safety evaluation of an orally active small molecule BoNT/A inhibitor.